postfix mail queue and backscatter

Well one of my servers got hit hard today in a couple of hours we have gotten over 30K emails to unknown recipients. My problem is postfix is accepting all of these emails into the mail queue then it generates bounces and of course those now sit in the queue. I have tweaked postfix with every known possible scenario on preventing backscatter and i know postfix by default is supposed to auto reject unkown recipients without accepting them into the mail queue, so why is my mail server acting like this? here is my main.cf